[FFmpeg-devel] [PATCH] HAM6/HAM8 support for IFF demuxer/decoder

[Sebastian Vater]

Peter Ross a ?crit :
> On Thu, Apr 29, 2010 at 02:11:25PM +0200, Sebastian Vater wrote:
>   
>> Michael Niedermayer a ?crit :
>>     
>>> On Thu, Apr 29, 2010 at 01:51:09PM +0200, Sebastian Vater wrote:
>>>   
>>>       
>>>> Michael Niedermayer a ?crit :
>>>>     
>>>>         
>>>>> On Thu, Apr 29, 2010 at 01:10:18PM +0200, Sebastian Vater wrote:
>>>>>   
>>>>>       
>>>>>           
>>>>>> Peter Ross a ?crit :
>>>>>>     
>>>>>>         
>>>>>>             
>>>>>>> On Wed, Apr 28, 2010 at 11:17:12PM +0200, Sebastian Vater wrote:
>>>>>>>   
>>>>>>>       
>>>>>>>           
>>>>>>>               
>>>>>>>> Sebastian Vater a ?crit :
>>>>>>>>     
>>>>>>>>         
>>>>>>>>             
>>>>>>>>                 
>>>>>>>>> So here is it!
>>>>>>>>>
>>>>>>>>> The long awaited HAM6/8 decoding support for IFF-ILBM.
>>>>>>>>>       
>>>>>>>>>           
>>>>>>>>>               
>>>>>>>>>                   
>>>>>>> Yep, glad somebody took the time.
>>>>>>>
>>>>>>>   
>>>>>>>       
>>>>>>>           
>>>>>>>               
>>>>>>>> +#define CAMG_EHB  0x80   // Extra HalfBrite
>>>>>>>>     
>>>>>>>>         
>>>>>>>>             
>>>>>>>>                 
>>>>>>> Macro isn't used.
>>>>>>>   
>>>>>>>       
>>>>>>>           
>>>>>>>               
>>>>>> Just added it, the next patch for EHB support will use it, should I
>>>>>> remove it until then and add the define when EHB is done?
>>>>>>
>>>>>>     
>>>>>>         
>>>>>>             
>>>>>>>   
>>>>>>>       
>>>>>>>           
>>>>>>>               
>>>>>>>> @@ -152,6 +157,12 @@ static int iff_read_header(AVFormatContext *s,
>>>>>>>>              st->codec->channels = (get_be32(pb) < 6) ? 1 : 2;
>>>>>>>>              break;
>>>>>>>>  
>>>>>>>> +        case ID_CAMG:
>>>>>>>> +            if (data_size < 4)
>>>>>>>> +                return AVERROR_INVALIDDATA;
>>>>>>>>     
>>>>>>>>         
>>>>>>>>             
>>>>>>>>                 
>>>>>>> Is this really neccessary. We dont check data_size for any of the other tags.
>>>>>>>   
>>>>>>>       
>>>>>>>           
>>>>>>>               
>>>>>> The IFF standard says that chunks can be of any length, it seems that
>>>>>> you missed by patch which does add the checking for other tags, too.
>>>>>>
>>>>>> Not checking such stuff could also cause security issues if someone with
>>>>>> a bad mind prepares an attack with a malformed IFF file.
>>>>>>
>>>>>> It would not be the first case picture decoders cause buffer overflows
>>>>>> thanks to malformed image data/structure. ;-)
>>>>>>
>>>>>> Also chunks can always be longer than the initial definition to it, just
>>>>>> like you can add new data fields to a struct. ;-)
>>>>>>
>>>>>> But in one point you're correct here, it should really be evaluated if
>>>>>> the decoder should abort if the chunk is to small (i.e. just 2 bytes,
>>>>>> because the amiga display mode used for it had a zero lower word) or
>>>>>> just consider to small stuff to be set to 0 (in that case non-HAM and
>>>>>> non-EHB would always be assumed).
>>>>>>
>>>>>>     
>>>>>>         
>>>>>>             
>>>>>>>> +        if (iff->camg_display_mode & CAMG_HAM) {
>>>>>>>> +            switch (st->codec->bits_per_coded_sample) {
>>>>>>>> +            case 6: // HAM6
>>>>>>>> +                st->codec->bits_per_coded_sample = 12; // 4096 color HAM6 image
>>>>>>>> +                break;
>>>>>>>> +
>>>>>>>> +            case 8: // HAM8
>>>>>>>> +                st->codec->bits_per_coded_sample = 18; // 262144 color HAM8 image
>>>>>>>> +                break;
>>>>>>>>     
>>>>>>>>         
>>>>>>>>             
>>>>>>>>                 
>>>>>>> My only concern here is that 'bits_per_coded_sample' is being abused to
>>>>>>> indicate both bpp *and* whether HAM coding is used. If somebody out there
>>>>>>> encodes 12-bit RGB into IFF then we will have a problem.
>>>>>>>   
>>>>>>>       
>>>>>>>           
>>>>>>>               
>>>>>> I just realized that too.
>>>>>>
>>>>>> And I'm just thinking of a better solution. Is it appreciated in ffmpeg
>>>>>> to use codec_tag as a bitfield or split up the uint32_t internally into
>>>>>> 4 uint8_t or 2 2 uint8_t's?
>>>>>>
>>>>>> Right now the IFF demuxer and decoder use codec_tag to store whether
>>>>>> it's an PBM or ILBM file.
>>>>>>
>>>>>> I would like to split it internally into 4 bytes and use one byte for
>>>>>> tagging if it's EHB/HAM, one byte for transparent color index, one byte
>>>>>> for the compression identifier and one byte for plane number being a
>>>>>> mask to skip.
>>>>>>     
>>>>>>         
>>>>>>             
>>>>> you would like to look at AVCodecContext.extradata
>>>>>
>>>>> [...]
>>>>>   
>>>>>       
>>>>>           
>>>> I know extradata, but it's used for the palette data already and moving
>>>> that data structures around or adding sth. at the end requires defining
>>>> a completely new structure (one for the palette data and one for extra
>>>> data).
>>>>
>>>> So I'ld use codec_tag for it, using an whole 32 bit integer just for
>>>> indicating if it's a PBM or ILBM (one bit would be enough for that) is
>>>> in my eyes, just a waste.
>>>>
>>>> Or are there any reasons for not doing it the way, I wrote my last msg?
>>>>     
>>>>         
>>> dont forget to fill AVIn/OutputFormat.codec_tag ;)
>>> (when you try you will see why the idea of spliting codec_tag like this
>>>  doesnt work)
>>>   
>>>       
>> Oh ok, I got the point. So it should always be a kind of fourcc, right?
>>     
>
> Yes, its meant to be a 'tag' for identification.
>
>   
>> Then I have to do this with extradata...
>>     
>
> Yep, just allocate a fixed length of bytes (for the flags) at the start
> of the extradata buffer and then append palette.
>   

Fixed! Please review attached patch.

-- 

Best regards,
                   :-) Basty/CDGS (-:

-------------- next part --------------
A non-text attachment was scrubbed...
Name: iff-ham-support.patch
Type: text/x-patch
Size: 10852 bytes
Desc: not available
URL: <http://lists.mplayerhq.hu/pipermail/ffmpeg-devel/attachments/20100504/529790eb/attachment.bin>